How common are avian diseases?

I'm a virologist (mostly flu), so I can answer for that and other viruses, but birds also host a range of bacterial and fungal and protozoan pathogens which can make you sick or even kill. These include things like salmonella (bacterial), chlamydia (bacterial), cryptosporidium (protozoan), aspergillus (fungal), and candida (yeast fungus)

In addition, birds often have things like lice and/or ticks that can host other infectious agents such as rickettsia, tularemia and a whole host of insect borne viruses.

The risk of getting ill depends on the type of bird, how abundant they are around you and how close the contact you are having is, and the type of disease - if you are handling dead or sick animals with bare hands and without washing your hands afterward, you are at great risk! Some infections will present with very obviously sick animals (e.g. highly pathogenic influenza), others are a part of the natural microflora of the species you are interacting with (e.g. salmonella), and as such the animals will often not show signs of infection.

Infections that have a zoonotic (come from animals) cause are relatively common, not least because many people have interactions with animals on a daily basis. A large portion of these zoonoses are a result of contamination of food stuffs with feces or from eating undercooked meat from an animal.

Having said that - what are the risks of feeding wild birds? Well, the answer is that we don't really know. Sometimes the risk will be higher than others, due to a wave of infection passing through the local population.

So, what do we know about infections in people who work closely with birds? Quite a lot for some diseases like salmonella and influenza, but not a lot for many other, less dramatic, diseases.

Immune surveys that investigate people who work with ducks and chickens in the wet markets of Asia show that they have somewhere between 0% and 10% prevalence for H5N1 ("bird flu", highly pathogenic often, summary in the paper linked) based on sero-conversion (this is the immune system recognizing the virus and protecting you against it), but this is only one strain of the range of influenza viruses and comprehensive studies are rare and difficult to conduct due to the ubiquity of influenza in the human population, so the actual number may be much higher once you take the other strains of influenza into account. The reason we can study H5 influenza is because it is not naturally found in humans - so we can look at the presence of antibodies and know that they came from a zoonotic event.

Now, this doesn't tell us much about the risk of getting sick - most of these people who have the antibodies against H5 didn't get sick and certainly weren't among the 1500 or so people who died from the virus.

Anyway, back to the point: If you see a sick animal, and particularly if you see a cluster of sick animals, it is best to avoid the birds for a while, and for the sake of your health - wash your hands!

posted almost 5 years ago

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bob1‭

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